Field of the Disclosure
The disclosure relates to a method of real-time measuring strain and related data by use of video methods.
Description of the Prior Art
Video extensometry is known in the prior art and well-developed for its intended purposes. However, a significant restrictive aspect of measuring strain with a video device is collecting the images at significant speed, providing the images to an image processing engine, processing the images to produce a displacement or strain value, outputting the strain value in a software consumable format and synchronizing it with other data collected via traditional real-time methods (e.g. load cells have electrically balanced bridges).
There are many manufacturers of video processing extensometers. Some of the major companies that provide these are Shimadzo, Zwick and Imetrum. Generally, all of these use the methodology of employing an external machine vision camera, inputting into the PC or video processing hardware and using hardware to convert the data to an electrical signal or having a software interface compatible with the materials testing system.
The prior art includes IPVE and AVE 1 which are manufactured by Instron and which are well developed for their intended purposes. These devices utilize an external camera, PC and analog outputs to capture images and process strain values from these images. The strain data is calculated by software in the PC and output via analog outputs. This is illustrated in FIG. 1.
There are many algorithms for calculating strain from a video images and each has advantages and disadvantages. The main drawback to most of the systems is they use an off-the-shelf high speed machine vision camera, transmit the images via a high speed bus to a processing system, manipulate the images using a standard or dedicated processing system such as a PC or microcontroller and then output the data internally to software on the processing system or via convertors to electrical signals. Typically these systems consume an entire image and work on the array of pixels to produce a strain or displacement value. Computing strain or displacement in this manner is computationally intensive and requires a large microprocessor system. Additionally, to guarantee real-time behavior in order to fulfill many materials testing needs, a real-time operating system is used on the processing system. After computation of the strain or displacement data, it is output to the software on a PC which requires a specialized interface and is not very portable or output via an analog or encoder device. These systems have issues with respect to time latency, integration and required computational power.